The proposal is for the purchase of an Optronics rotating drum film scanner. This is to replace our current scanner which is so old that many of its component parts can no longer be replaced. The scanner is central in the processing of X-ray diffraction diagrams used in the analysis of the three-dimensional structure determination of crystalline proteins and viruses. At this time a number of projects are in progress at Purdue University. These are the structure determination of southern bean mosaic virus, cowpea mosaic virus, belladonna mottle virus, phosphoglucomutase, nitrogenase, catalase, lactate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, quinolinate phosphoribosyltransferase and various fibrous nucleic acids and polysaccharides. The primary (but not only) mode of X-ray diffraction photography is the oscillation method which enables us to determine the intensities of over 10,000 X-ray reflections on any one film. The programs used at Purdue for the analyses of these photographs were developed and written by the principal investigator.